Maintenance Agents Flashcards
1
Q
What is inhalation anaesthesia?
A
- Induction: Usually with an injectable and can be with a gas
- Maintenance: Usually with an inhalational agent and can with injectable
- For both: Part of the gas provided in nitrous oxide or a liquid vaporised into the mixed gas
2
Q
What are volatile agents?
A
- Liquid anaesthetic agents that are vaporised into gases, which are then inhaled by the patient
- A vaporiser is a device that adds volatile agent to a carrier gas
3
Q
What are the ideal properties of volatile agents?
A
- Chemically stable
- Non-flammable
- No environmental hazard
- Inexpensive
- High potency
- Low blood solubility
- Minimal metabolism
- Minimal toxicity
- No cardiorespiratory side effects
- Analgesia
- Easily administered
4
Q
What are the advantages of inhalation agents?
A
- Administered in oxygen through ET tube
- Rapid action
- Change in depth of anaesthetic rapid
- Rapid recovery
5
Q
What are the disadvantages of inhalation agents?
A
- Anaesthetic machine costly and requires full understanding by user
- Workplace pollution
- Dose dependent cardiopulmonary depression
6
Q
What are the pharmocokinetics of inhalation agents?
A
- Agent is inhaled and passed into lungs
- Diffuses into the pulmonary circulation
- Travels around the body via the circulatory system and is distributed to the tissues
- Depending on agent solubility, it will diffuse back into the blood and be eliminated by the lungs
7
Q
What are the factors that affect gaseous uptake?
A
- Inspired concentrations of the agent
- Alveolar concentration
8
Q
How do inspired concentrations affect gaseous uptake?
A
- Vaporiser setting: the higher the % on the dial, the more concentrated the volatile agents
- FGF: a high FGF will affect the volume of volatile agents in a rebreathing system
- Function of the breathing system: rebreathing systems are bulky and have lots of components meaning that it takes longer for higher concentrations to be reached
9
Q
What is alveolar concentration?
A
- This is the partial pressure
- Used as a blood: gas partition coefficient
- Reliant on good alevolar ventilation and pulmonary circulation
10
Q
What is the blood : gas partition coefficient?
A
- The measure of the distribution of the inhalation agent between the blood and gas phases within the body
- Low solubility: does not dissolve in the blood so rapid induction and recovery
- High solubility: dissolves more readily in the blood, so slow induction and recovery
11
Q
What is potency?
A
- Is expressed as the minimum alveolar concentration (MAC value)
12
Q
What is a MAC value?
A
- The amount of volatile gas that is needed to keep 50% of patients asleep when exposed to a standard noxious stimuli
13
Q
What increases the MAC value?
A
- Hyperthermia
- Catecholamines
- Hyperthyroidism
- Hypernatremia
14
Q
What decreases the MAC value?
A
- Hypothermia
- Hypoxaemia
- Hypercapnia
- Drugs that affect CNS
- Analgesia agents
- Pregnancy
- Old age
- Hypotension
- Hypothyroidism
15
Q
What factors affect the elimination of inhalants?
A
- CNS concentrations low enough, the patient will start to regain consciousness
- Newer gases almost 100% eliminated through exhalation
- Older gases 25% is metabolised
- Removal of agent is determined by B : G pCE
- Can speed up elimination in rebreathing system by turning off the gas and increasing the oxygen flow
16
Q
What is the inhalant effect on the cerebrum?
A
- Decrease metabolic rate
- Decrease in cerebral oxygen concentration
- Decrease in cerebral blood flow
-Cerebral vasodilation - Increase in blood volume
17
Q
What is the inhalant effect on the cardiovascular system?
A
- CV depression is a major side
- This is dose dependent
-Cardiac output, systemic vascular resistance and arterial BP, due to decreased myocardial contractility and vasodilation
18
Q
What is the inhalant effect on the respiratory system?
A
- Dose dependent respiratory depression
- Could lead to hypercapnia
- Decrease in minute volume
- Decrease in respiratory rate
- Decrease in tidal volume
19
Q
What is the inhalant effect on the renal and hepatic system?
A
- Perfusion is decreased due to hypotension
- Renal perfusion issues may lead to decreased urine output
- Sevoflurane with rebreathing systems can react with soda-line, which makes compound A (is nephrotoxic in rats)
- Decreased perfusion to the liver may lead to decreased drug metabolism
20
Q
What is halothane?
A
- Very potent halogenated hydrocarbon
- Requires preservative
- Does not decompose in presence of warm soda lime
- Respiratory and cardiovascular depressant
- Metabolised by liver (20-25%)
21
Q
What is isoflurane?
A
- Fluorinated ether
- Very potent
- Delivered using a precision out of circuit vaporiser
- Strong pungent colour
- Respiratory and cardiovascular depressant
- Low solubility
- Under 1% metabolised by patient
22
Q
What is sevoflurane?
A
- Fluorinated ether
- Slightly less potent than isoflurane
- Requires different vaporiser to isolflurane
- Metabolised to produce fluoride ions
- Less soluble than isoflurane
- Cardiovascular and respiratory depressant
- 3% metabolised
23
Q
What is desflurane?
A
- Fluorinated ether
- Needs specialised vaporiser
- Expensive
24
Q
What is nitrous oxide?
A
- Gaseous inhalant
- Used in combo with more potent inhalant such as halothane
- Low solubility so rapid transfer
- Cannot achieve true anaesthesia alone as MAC values are high
25
Q
What are the side effects of using nitrous oxide?
A
- Mild sympathetic stimulation
- Diffuses into gas filled spaces
- Diffusion hypoxia, so adequate oxygen required during recovery
26
Q
What is the nitrous oxide second gas effect?
A
- Nitrous oxide will increase the rate of uptake of other inhalational agents into the blood stream and therefore an appropriate level of anaesthesia will be reached more quickly
27
Q
What is nitrous oxide diffusion hypoxia?
A
- Caused by rapid movement of gas
- When recovering, nitrous oxide should be switched off and and oxygen should be maintained
- if not, oxygen can reach dangerously low levels in alveoli as nitrous diffuses out of blood stream
28
Q
What is occupational exposure?
A
- Gas leaking into the room, due to disconnection of the patient and not flushing out the anaesthetic circuit, poorly fitted mask, underinflated ETT cuff and during recovery from GA
- Can causes mutagenic, carcinogenic and teratogenic effects
29
Q
What are the inhalational exposure issues?
A
- Spontaneous abortion
- Fertility issues
- Minor congenital abnormalities
- Leukaemia and lymphoma
- Liver/renal disease
- Effects on the immune system
